This double-blind cross-over randomized clinical trial will compare the bioavailability of Mg from Mg chelate to that of Mg from MgO in Crohn's disease patients who have had ileal resections. The unique feature of this study is the use of 25-Mg labeled Mg chelate of MgO to study absorption. Use of stable isotopes will allow us to compare the postabsorptive retention of 25-Mg as well as erythrocyte and mononuclear cell 25-Mg incorporation to yield an overall picture of Mg availability.